The present invention relates to multilevel memory system, and more particularly relates to adjustable reference and margin levels for multilevel memory systems.
As information technology progresses at an unprecedented pace, the need for information storage increases proportionately. Accordingly, the non volatile information in stationary or portable communication demands higher capability and capacity storage. One approach to increasing the amount of storage is by decreasing physical dimensions of the stored bit (e.g., memory cell) to smaller dimensions such as nanocell technology. Another approach is to increase the storage density per bit. The second approach is known as digital multilevel nonvolatile storage technology. A sense amplifier reads the content of a memory cell by comparison to reference levels. As more bits are stored in a multilevel memory cell, the voltage separation of reference level cells decreases. Variation within the memory cell, the sense amplifier, and other circuits may change reference levels to cause erroneous detection of the content of a memory cell.